GB2309623A

GB2309623A - Structures for use in reinforcing earthworks

Info

Publication number: GB2309623A
Application number: GB9623223A
Authority: GB
Inventors: Austin Knight
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-02-02
Filing date: 1996-11-07
Publication date: 1997-08-06
Also published as: GB9602138D0; GB9623223D0

Abstract

A flexible structure for reinforcing earthworks comprises a porous membrane with grass rooted therein and may also include a layer of fertile material below the membrane. The membrane may be formed of a fibrous synthetic material such as polypropylene. The flexible structure may overlay or underlay a perforate wall of a rigid container filled with a fertile material. The containers may be used to provide support for vegetation over the surface of steeply inclined earthworks.

Description

STRUCTURES FOR USE IN REINFORCING EARTHWORKS This invention relates to structures for use in reinforcing earthworks formed by excavation or otherwise.

It relates particularly, but not exclusively to the use of such structures to provide turf over earthworks-.

Man-made earthworks such as embankments, for example, are inherently unstable when first constructed and vulnerable to erosion by the weather. In order to retain the earth in position, mechanical elements can be installed within the body of earth. Often for aesthetic reasons, newly-formed earthworks are also sown with grass seed. However, grass seed typically take several weeks to germinate and grow. Alternatively, turf in which grass is already established may be laid over the earthworks or earth surface. Such turf is relatively expensive and costly to handle and transport, and does little to stabilise the earthworks. The mechanical elements referred to above are also expensive. In addition, it is particularly difficult to establish any significant grass growth over steep faces of earthworks.

Steeply inclined or vertical faces of embankments or other earthworks are often reinforced using metal cages filled with broken rock or other loose material.

However, earth and grass seed are easily removed by weathering from such structures.

The present invention provides a flexible structure comprising a porous membrane with grass rooted therein. The flexible structure may include a layer of fertile material above and/or below the membrane to ensure the grass is well established in the structure.

The membrane is preferably formed of fibrous synthetic material, and a particular preferred material for forming the membrane is polypropylene. Membranes or textiles of synthetic material suitable for use in the present invention are typically used in drainage applications within earthworks, or to reinforce earthworks by being laid over successive strata as the structure is built up.

Such membranes are often referred to as "geo-textiles't.

These flexible structures of the invention are considerably lighter and more resilient than conventional turf by virtue of their reinforcing membrane, and as a consequence, are easier to handle and transport. In addition the porous membrane can be selected to provide the turf with particular stress, strain and durability characteristics as appropriate, with an inherent tensile strength. A suitable membrane is formed of W-stabilised polypropylene. Such products are available from Polyfelt GmbH of Ling, Austria, and can be plain felts or felts reinforced with a backing web.

The invention further provides a substantially rigid container filled with fertile material and having a perforate wall, with a flexible structure of the invention overlying or underlying the wall. At least one support member may extend across the container to strengthen it. The container is preferably in the shape of a cuboid. Containers of the invention may be used to provide vegetation over the surface of steeply inclined earthworks, giving a more attractive appearance.

According to the invention, a method of producing a flexible structure comprises the steps of laying a porous membrane on a support; distributing grass seed over one side of the membrane; and growing grass on the membrane. Preferably, the grass seed has germinated prior to its distribution over the membrane.

Furthermore, it may be preferable to lay the permeable membrane over the support before the porous membrane.

This can assist the grass growth by retaining more water for the grass. If desired, the porous membrane may be laid over a substrate of fertile material. Also fertile material may be laid over the membrane prior to the distribution of seed thereon. Alternatively, the step of distributing grass seed may comprise distributing a mixture of grass seed and fertile material over the one side of the membrane.

Using pre-germinated seed, it typically takes two weeks for grass to become established in the membrane of a flexible structure according to the invention.

Using seed that has not been pre-germinated, the period is six to twelve weeks. The structure may then be rolled up and transported to the site of the respective earthworks. Once incorporated in an earth structure, the grass continues to grow and the roots propagate into the structure. Thus, in use of the flexible structure, the grass and the membrane in combination hold the form of the earthworks, and minimise the erosive effects of the weather.

In some applications, it may be preferable to include a layer of soil, compost, coniferous bark, peat, mulch or other fertile material above and/or below the membrane before sowing the seeds onto it. The grass roots then bind the fertile material to the membrane.

The depth of a layer is preferably about 1.2cm. A suitable form of coniferous bark can be obtained from Melcourt Industries of Tetbury. It has also been found that grass seed can grow satisfactorily on a moist synthetic membrane alone, particularly if the seeds have already germinated before they are distributed over the membrane. However, the grass can survive longer periods rolled up in the membrane for transportation if fertile material is included in the structure.

Although the above description relates to growing grass on a porous membrane, it will be appreciated that other plants can be grown on such a membrane in accordance with the invention. Also, turf of the invention can not only be used to reinforce earth structures but also in place of conventional turf, on lawns for example. It is also suitable for sports grounds, and playing and running surfaces, and can be used for example as a training or even a racing surface for dogs or horses.

The container of the invention, which incorporates the flexible structure described above, enables steeply-sided or even vertical earth structures to be formed with a covering of grass or other plants.

They are preferably in the form of cuboid units so they can be readily stacked or arranged as appropriate. Each container can be constructed by fastening together rigid sheets of wire mesh using ring chips or wires. Typical dimensions are 1 by 0.5 by 0.2m. However, it will be appreciated that a range of three dimensional shapes may be formed as appropriate.

Each container may be split into compartments by internal dividing members which provide additional strength. Pre-formed fibre boxes can be placed in each compartment, filled with fertile material. Fertile material is used to enable the grass or other plants growing on the structure to become well established. The bulk material may be compacted in the fibre boxes to ensure that no further settlement or displacement of the material occurs once the units are in position.

The flexible structure described above provides vegetation over one or more perforate walls of each rigid container. It can be laid over the outer surface of the container, and in time, the grass will become firmly rooted into the fertile material. Alternatively, the flexible structure can be used to line the inner surface of one or more perforate walls of the container, with the grass growing through the wall(s).

The containers can be employed in a wide range of applications to provide a rigid structure with a covering of vegetation. As noted above, they can provide a pre-grown facing over gabion or bastion structures.

They can also be laid over banks or slopes to prevent erosion through weathering. Furthermore, they can be fastened together to form vegetated walls or sound barriers, using an appropriate support arrangement. A vegetated rugged platform or walkway may be formed by laying the containers over the ground.

The perforate wall of the containers is preferably formed from corrosion resistant material or another material coated with corrosion resistant material. For example a wire mesh wall may be formed of stainless steel, or of iron coated with zinc, bezinal or PVC. Mesh of these types is available from Gridweld of Wigan. It will be apparent that any form of durable, planar and perforate material can be used which allows the grass, or grass roots to grow therethrough.

Claims

CLAIMS:

1. A flexible structure comprising a porous membrane with grass rooted therein.

2. A flexible structure according to Claim 1 including a layer of fertile material below the membrane.

3. A flexible structure according to Claim 1 or Claim 2 including a layer of fertile material above the membrane.

4. A flexible structure according to any preceding Claim wherein the membrane is formed of fibrous synthetic material.

5. A flexible structure according to any preceding Claim wherein the membrane comprises polypropylene.

6. A flexible structure substantially as described herein.

7. A substantially rigid container filled with fertile material and having a perforate wall, with a flexible structure according to any preceding claim overlying the wall.

8. A substantially rigid container filled with fertile material and having a perforate wall, with a flexible structure according to any Claims 1 to 6 underlying the wall.

9. A container according to Claim 7 or Claim 8 wherein at least one support member extends across the container to strengthen it.

10. A container according to any of Claims 7 to 9 in the shape of a cuboid.

11. A container substantially as described herein.

12. A method of producing a flexible structure according to any of Claims 1 to 6, comprising the steps of laying a porous membrane on a support; distributing grass seed over one side of the membrane; and growing grass on the membrane.

13. A method according to Claim 12 wherein germinated grass seed is distributed over the membrane.

14. A method according to Claim 12 or Claim 13 wherein a permeable membrane is laid on the support before the porous membrane.

15. A method according to any of Claims 12 to 14 wherein prior to the step of distributing grass seed, a layer of fertile material is laid over the membrane.

16. A method according to any of Claims 12 to 14 wherein the step of distributing grass seed comprises distributing a mixture of grass seed and fertile material over the one side of the membrane.

17. A method according to any of Claims 12 to 16 wherein the porous membrane is laid over a substrate of fertile material.

18. A method of producing a flexible structure substantially as described herein.

19. A flexible structure according to Claim 2 or Claim 3, a container according to any of Claims 7 to 11 or a method according to any of Claims 15 to 17 wherein the fertile material comprises tree bark or fertiliser or both.